1. Field of the Invention
The present invention relates to selecting cards for Jacquard-type equipment. More specifically, the present invention relates to a piezoelectric actuated selecting card for use in a Jacquard loom.
2. Description of the Prior Art
The use of Jacquard selection devices in weaving looms to produce intricate patterns by controlling the lifting of selected warp yarns is well known in the art. The separation formed between the lifted warp yarns and the non-lifted warp yarns is referred to as the shed. The Jacquard mechanism allows for independent movement of each warp yarn by controlling hooks (latches, catches) which engage matching hooks on rods (healds) connected to each warp yarn in a harness. A lifting device (or board) is used to raise or lower those warps in the harness whose corresponding hooks have been engaged. By coordinating the movement of the hooks, sequences of warp yarns can be selected and lifted while filling yarns are passed through the shed. In this manner, the Jacquard selection device is used to create the woven pattern.
Jacquard selection devices can be used in looms in either a closed shed or an open shed arrangement. In the closed shed arrangement, a single lifting device having an engaging hook for each warp in the harness is used. Whereas, the open shed configuration uses a double hook system of two lifting devices which provide pairs of engaging hooks which connect with pairs of (ascending and descending) rods that lift a single warp. The open shed configuration has two lifting devices and requires only a single move of each lifting device to create the shed, while the closed shed configuration has one lifting device but requires two moves.
Historically, the Jacquard mechanism involved a paper selection card having a pattern of punched holes. The selection card would allow those rods (or hooks) located at a hole to pass through and lift the corresponding warps, whereas the rods would be blocked at the locations without holes. By changing or shifting the selection card after each pass, the weave pattern could be formed.
This process was mechanically complex and often led to breakdowns and fabric quality problems. The mechanical complexity has been a major obstacle to increasing the efficiency of Jacquard machines. In response, several electrically selected loom latches have been proposed. For example, U.S. Pat. No. 6,073,662 to Herbepin, which is incorporated herein by reference, teaches the use of an electromagnetic device having a coil to control the position of each catch relative to a corresponding hook in a Jacquard selection device. When an electromagnet device is powered, the attached catch is positioned to engage the corresponding hook. The shed is opened by operation of a lifting board. Despite such proposed solutions, electrical and electromagnetic selection devices remain relatively large in comparison to the scale of the weave pattern.
A refinement of this electrical approach has been the application of piezoelectric elements to Jacquard selection devices. Piezoelectric actuator elements are devices that produce a lateral or longitudinal displacement with a high force capability when an operating voltage is applied. There are many applications where a piezoelectric actuator may be used, such as ultra-precise positioning and the generation/handling of high forces or pressures in static or dynamic situations.
Actuator configuration can vary greatly depending on application. For example, a flexure strip of piezoelectric material can be used to produce a transverse displacement. Piezoelectrics can also be stacked together to increase the displacement.
These devices are especially useful for controlling vibration, positioning applications and quick switching. For example, piezoelectric actuators can be designed to produce strokes of several micrometers at ultrasonic (>20 kHz) frequencies.
The critical specifications for piezoelectric actuators are the displacement, force and operating voltage of the actuator. Other factors to consider are stifffiess, resonant frequency and capacitance. Stiffness is a term used to describe the force needed to achieve a certain deformation of a structure. For piezoelectric actuators, it is the force needed to elongate the device by a certain amount.
Numerous approaches have been proposed to improve the operation of Jacquard-type weaving machines by incorporating piezoelectric elements. For example, U.S. Pat. No. 5,392,818 to Seiler discloses a needle selector for a Jacquard weaving machine similar to prior art mechanical devices only using piezoelectric transducers to adjust each blocking element. U.S. Pat. No. 6,470,919 to Wardle discloses an individual warp selector wherein a piezoelectric element drives a motor which mechanically moves a rigid heald. U.S. Pat. No. 5,464,046 to McIntyre discloses another individual warp selector wherein a piezoelectric element mechanically slides a warp selector in the longitudinal direction. U.S. Pat. No. 5,647,403 to Willbanks discloses using a piezoelectric element as a mechanical brake on the movement of a Jacquard warp selector. U.K. Patent No. GB 2 276 637 to Seiler and U.S. Pat. No. 5,666,999 to Dewispelaere disclose using piezoelectric elements as controls (locks) on the movement of catches for engaging lifting hooks in an open shed loom arrangement. However, each of these approaches simply uses the piezoelectric element to activate the mechanical elements which select the warp yarns. Because these approaches retain many of the complex mechanical features of the prior art, they exhibit many of the same limitations. For example, the size of these devices is not amenable to weaving high density patterns.
Therefore, a need exists for a Jacquard selection device which is mechanically reliable, operates at high-speed, has low power consumption, and is small enough to provide for high density warp selection.
The present invention provides a solution to the problem of providing a high density Jacquard selection device which is high-speed, reliable, and low power.